Simplify the following expression: $\dfrac{28y}{70y^4}$ You can assume $y \neq 0$.
Explanation: $ \dfrac{28y}{70y^4} = \dfrac{28}{70} \cdot \dfrac{y}{y^4} $ To simplify $\frac{28}{70}$ , find the greatest common factor (GCD) of $28$ and $70$ $28 = 2 \cdot 2 \cdot 7$ $70 = 2 \cdot 5 \cdot 7$ $ \mbox{GCD}(28, 70) = 2 \cdot 7 = 14 $ $ \dfrac{28}{70} \cdot \dfrac{y}{y^4} = \dfrac{14 \cdot 2}{14 \cdot 5} \cdot \dfrac{y}{y^4} $ $\phantom{ \dfrac{28}{70} \cdot \dfrac{1}{4}} = \dfrac{2}{5} \cdot \dfrac{y}{y^4} $ $ \dfrac{y}{y^4} = \dfrac{y}{y \cdot y \cdot y \cdot y} = \dfrac{1}{y^3} $ $ \dfrac{2}{5} \cdot \dfrac{1}{y^3} = \dfrac{2}{5y^3} $